The early evolutionary history of neo-sex chromosomes in Neotropical grasshoppers, Boliviacris noroestensis (Orthoptera: Acrididae: Melanoplinae)

Neo-sex chromosomes are an important component of chromosome variation in Orthoptera, particularly South American Melanoplinae species, which have proven to be outstanding experimental model system to study the mechanism of sex chromosome evolution in this group of insects. In terms of their origin, most derived sex chromosome mechanisms involve a Robertsonian fusion (i.e. translocation) between the ancestral X chromosome and an autosome. In the grasshopper, Boliviacris noroestensis Ronderos & Cigliano (1990) (Orthoptera: Acrididae: Melanoplinae), our results point to a small degree of differentiation (conserved homology between the XR arm and the neo-Y) of the neo-XY chromosomes, which may be of recent evolutionary origin. However, a simple centric fusion model does not explain their origin, mainly because of the observed reduction in the fundamental number (FN) of arms. We propose two models which, we hope, clarify the genesis of B. noroestensis neo-sex chromosomes. Records of karyotype variation in related species due to multiple rearrangements support our models. We propose a possible adaptive advantage for neo-sex chromosome carriers, such changes perhaps representing the primary force that increases their frequency within natural populations compared with non-fused translocated forms, and occurring without apparent detriment to the microevolutionary forces that may also act, at least at the beginning of the evolutionary history of individuals bearing such neo-sex chromosomes.Fil: Castillo, Elio Rodrigo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas; ArgentinaFil: Taffarel, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas; ArgentinaFil: Marti, Dardo Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas; Argentin

The central-marginal hypothesis in acridid Orthoptera: a critique of Colombo's (2012) article

We discuss and criticise the contention of Colombo (2012) that the central-marginal model does not apply to three species of chromosomally polymorphic acridid grasshoppers, and that chromosomal clines in these species are a consequence of temperature gradients. We also discuss Colombo's interpretation of our own results on the South American melanopline grasshopper, Dichroplus pratensis Bruner.Fil: Bidau, Claudio Juan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Misiones. Facultad de Ciencias Exactas, Químicas y Naturales; ArgentinaFil: Marti, Dardo Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Universidad Nacional de Misiones. Instituto de Biología Subtropical; Argentina. Universidad Nacional de Misiones. Facultad de Ciencias Exactas, Químicas y Naturales; Argentin

B chromosomes and Robertsonian fusions of Dichroplus pratensis (Acrididae): intraspecific support for the centromeric drive theory

We tested the centromeric drive theory of karyotypic evolution in the grasshopper Dichroplus pratensis, which is simultaneously polymorphic for eight Robertsonian fusions and two classes of B chromosomes. A logistic regression analysis performed on 53 natural populations from Argentina revealed that B chromosomes are more probably found in populations with a higher proportion of acrocentric chromosomes, as the theory predicts. Furthermore, frequencies of B-carrying individuals are significantly negatively correlated with the mean frequency of different Robertsonian fusions per individual. No significant correlations between presence/absence or frequency of Bs, and latitude or altitude of the sampled populations, were found. We thus provide the first intraspecific evidence supporting the centromeric drive theory in relation to the establishment of B chromosomes in natural populations.Fil: Bidau, Claudio Juan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Misiones. Facultad de Humanidades y Ciencias Sociales. Departamento de Genética. Laboratorio de Genética Evolutiva y Molecular; ArgentinaFil: Marti, Dardo Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Universidad Nacional de Misiones. Instituto de Biología Subtropical; Argentin

Contrasting patterns of sexual size dimorphism in the grasshoppers Dichroplus vittatus and D. pratensis (Acrididae, Melanoplinae)

Sexual size dimorphism (SSD) can be the result of sexual selection (SS) or natural selection (NS). Due to male-male competition for access to females, SS could favor an increase in male body size. On the other hand, larger size in females could be favored by NS, since egg production is directly correlated with body size. Rensch`s rule states that SSD increases with increasing body size in animals, where males are the larger sex, and decreases when females are larger than males. Thus, Rensch’s rule predicts that in those insects where females are larger than males, SSD should decrease with increasing body size, when comparing populations and species. We analyzed SSD in 19 Argentine populations of the grasshoppers Dichroplus vittatus and 25 of D. pratensis. Both species show latitudinal and altitudinal variation in body size, following the converse to Bergmann’s rule: body size decreases with increasing latitude and decreasing ambient temperature. SSD occurs in both species across their geographical distribution ranges, also involving differences in allometry and shorter developmental times in males. In D. vittatus, the degree of SSD increased significantly with general body size, whereas in D. pratensis SSD decreased as body size increased. A plausible explanation of SSD is that SS favors a differential increase in female body size related to a preference by males for more fecund females. Given the close phylogenetic relationship between both species, the differences in SSD between them may be the result of differential natural and sexual selective pressures. In D. vittatus both sexes could be reacting differently to environmental conditions regarding body size, while in D. pratensis protandry could be the main factor behind SSD.Fil: Bidau, Claudio Juan. Instituto Oswaldo Cruz; BrasilFil: Marti, Dardo Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas; Argentin

Chromosome fusion polymorphisms in the grasshopper, Dichroplus fuscus (Orthoptera: Acrididae: Melanoplinae): Insights on meiotic effects

Robertsonian changes account for many of the changes in the evolution of the orthopteran karyotype; in their origin, a centric fusion is involved between two acro-telocentric chromosomes, forming a single bi-armed chromosome. It is usual for these rearrangements to be associated with profound changes in meiosis, such as modification in frequency and distribution of chiasmata. Dichroplus fuscus is a South American grasshopper with a wide distribution. In this work we analyzed nine populations from Misiones Province, north-eastern Argentina. This species presents a standard karyotype of 2n = 23/24 (♂/♀) with all chromosomes acro-telocentric and an X0/XX chromosomal sex determining mechanism. This standard karyotype has been modified by the occurrence of two Robertsonian fusions involving chromosomes 1/3 and 2/4; values of fusions per individual (fpi) show a significant increase in the presence of karyotypic polymorphisms towards southern populations. In individuals showing chromosomal rearrangements, we observed a clear redistribution of chiasmata towards distal positions; significant differences were noted between Robertsonian homozygotes (Ho) and heterozygotes (Ht) for chromosomes arms L1 and M3, although this was not the case between Ho and Ht for chromosomes L2 and M4. With regard to the orientation of trivalents, values obtained for non-convergent orientation were low.Fil: Taffarel, Alberto. Provincia de Misiones. Comité de Desarrollo e Innovación Tecnológica. Centro de Desarrollo e Innovación Tecnológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas; ArgentinaFil: Bidau, Claudio Juan. Universidad Nacional de Misiones; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Marti, Dardo Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas; Argentin

Rensch's rule is not verifiedin melanopline grasshoppers (Acrididae)

Sexual size dimorphism (SSD) is almost universal in animals. Rensch?s rule proposes that SSD increases with increasing average body size in taxa where males are larger than females (male- biased SSD; MBSSD) and decreases when females are larger (femalebiased SSD; FBSSD). Although it was proposed thatboth patterns are part of the same evolutionary trend, there is more evidence for Rensch?s rule in the first case. We analyzed SSD in the acridid subfamily Melanoplinae ina sample of 718 species and subspecies covering all tribes and representative genera. As in all Orthopera, SSD is female-biased. Body length was used as a proxy for body size. Mean body size within the subfamily varied between 9 and 34.5 mm in males (N= 812) and 12.75 and 44.0 mm in females (N= 735). Except for five species (0.7%) all taxa (from subfamily to subspecies) showed moderate to strong FBSSD (mean= 1.27). The lowest SSD was observed in Melanoplus chumash(SSD= 1.01), and the highest in Phaedrotettix aptera coquinae(SSD= 1.83). To test Rensch?s rule we performed reduced major axis (RMA) regressions between log10 (male body length) and log10 (female body length). In no case RMA slopes were significantly higher than 1.0 which would signal Rensch?s rule. Thus, Melanoplinae representsa new case of FBSSD where Rensch?s rule is not verified. The proximatecauses of FBSSD and the non-occurrence of Rensch?s rule in the Orthoptera are discussed as well as the relationship between SSD patterns at the intra- and supraspecific levels.Fil: Bidau, Claudio Juan. Universidad Nacional de Rio Negro; ArgentinaFil: Marti, Dardo Andrea. Universidad Nacional de Misiones. Facultad de Humanidades y Cs.sociales. Departamento de Genetica. Laboratorio de Genetica Evolutiva y Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Castillo, Elio Rodrigo Daniel. Universidad Nacional de Misiones. Facultad de Humanidades y Cs.sociales. Departamento de Genetica. Laboratorio de Genetica Evolutiva y Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Cytogenetic analysis on geographically distant parthenogenetic populations of Tityus trivittatus Kraepelin, 1898 (Scorpiones, Buthidae): karyotype, constitutive heterochromatin and rDNA localization

Tityus trivittatus Kraepelin, 1898 is the most medically important scorpion species of Argentina, and parthenogenetic populations are present in the major cities of this country. We performed a detailed cytogenetic analysis of specimens of three synanthropic parthenogenetic populations, all distant about 900 km from each other, using Ag-NOR, C-banding, DAPI/CMA3 staining and FISH with autologous 28S rDNA probes. The karyotype of females and embryos from the three populations showed 2n=6, with two large and four middle-sized holokinetic chromosomes. Constitutive heterochromatin was found in terminal and interstitial location and its pattern allowed the identification of three chromosome pairs. NORs were found on the terminal heterochromatic region of one pair of middle-sized chromosomes. The use of fluorochromes to characterize heterochromatin showed the absence of GC-rich heterochromatin and a low and variable number of AT-rich heterochromatic regions. We propose that a possible explanation for the lack of karyotypic variation between these geographically distant populations could be a recent colonization of urban areas by human means of synanthropic specimens from a single lineage of northeastern Argentina.Fil: Adilardi, Renzo Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Ojanguren Affilastro, Andres Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Pque. Centenario. Museo Argentino de Ciencias Naturales "bernardino Rivadavia". Departamento de Invertebrados. Area de Entomologia; ArgentinaFil: Marti, Dardo Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas; ArgentinaFil: Mola, Liliana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

Genomic Differences Between the Sexes in a Fish Species Seen Through Satellite DNAs

Neotropical fishes have highly diversified karyotypic and genomic characteristics and present many diverse sex chromosome systems, with various degrees of sex chromosome differentiation. Knowledge on their sex-specific composition and evolution, however, is still limited. Satellite DNAs (satDNAs) are tandemly repeated sequences with pervasive genomic distribution and distinctive evolutionary pathways, and investigating satDNA content might shed light into how genome architecture is organized in fishes and in their sex chromosomes. The present study investigated the satellitome of Megaleporinus elongatus, a freshwater fish with a proposed Z1Z1Z2Z2/Z1W1Z2W2 multiple sex chromosome system that encompasses a highly heterochromatic and differentiated W1 chromosome. The species satellitome comprises of 140 different satDNA families, including previously isolated sequences and new families found in this study. This diversity is remarkable considering the relatively low proportion that satDNAs generally account for the M. elongatus genome (around only 5%). Differences between the sexes in regards of satDNA content were also evidenced, as these sequences are 14% more abundant in the female genome. The occurrence of sex-biased signatures of satDNA evolution in the species is tightly linked to satellite enrichment associated with W1 in females. Although both sexes share practically all satDNAs, the overall massive amplification of only a few of them accompanied the W1 differentiation. We also investigated the expansion and diversification of the two most abundant satDNAs of M. elongatus, MelSat01-36 and MelSat02-26, both highly amplified sequences in W1 and, in MelSat02-26’s case, also harbored by Z2 and W2 chromosomes. We compared their occurrences in M. elongatus and the sister species M. macrocephalus (with a standard ZW sex chromosome system) and concluded that both satDNAs have led to the formation of highly amplified arrays in both species; however, they formed species-specific organization on female-restricted sex chromosomes. Our results show how satDNA composition is highly diversified in M. elongatus, in which their accumulation is significantly contributing to W1 differentiation and not satDNA diversity per se. Also, the evolutionary behavior of these repeats may be associated with genome plasticity and satDNA variability between the sexes and between closely related species, influencing how seemingly homeologous heteromorphic sex chromosomes undergo independent satDNA evolution.Fil: Crepaldi, Carolina. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Martí, Emiliano. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Gonçalves, Évelin Mariani. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Marti, Dardo Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Universidad Nacional de Misiones. Instituto de Biología Subtropical; ArgentinaFil: Parise Maltempi, Patricia Pasquali. Universidade Estadual Paulista Julio de Mesquita Filho; Brasi

Fluctuación poblacional de Culicoides insignis (Diptera: Ceratopogonidae) en Posadas, Misiones, Argentina

The Bluetongue virus appears to be restricted in Argentina to the northeasternarea of the country. In the Neotropical region the main vector could be Culicoides insignis Lutz. This study was aimed to determine the population fluctuation of C. insignis in Posadas city and test the influence of climatic variables as determinants of the abundance of this species. The specimens were collected in Posadas city using CDC light traps from January to December 2013. The abundance of C. insignis in relation to environmental variables was analyzed using multivariate linear regression. A total of 2,952 specimens of C. insigniswere collected representing 93.4% of the total Culicoides captured. The multivariate linear regression analyses show that the monthly mean relative humidity was the variable that best explained the population dynamics of C. insignis in the work area. The pathogen transmission is probably influenced by the abundance of the vector in this area. The population peaks observed are indicative of periods when there should be more control to prevent transmissionof the disease. This is the first report of population fluctuation of C. insignis in northeastern Argentina.En Argentina, la distribución de la enfermedad del Virus de la Lengua Azul se encuentra restringida al noreste del país. En la región Neotropical el principal vector sería Culicoides insignis Lutz. El objetivo de este trabajo fue determinar la fluctuación poblacional de C. insignis en la ciudad de Posadas y también la influencia de las variables climáticas como determinantes en la abundancia de esta especie. Los ejemplares fueron capturados mediante trampas de luz en el período comprendido entre enero y diciembre de 2013. La relación entre el número de C. insignis capturados y las variables ambientales fue analizada por regresión lineal multivariada. Se recolectaron 2.952 ejemplares de C. insignis representando el 93,4% del total de Culicoides capturados. Los análisis de regresión lineal multivariada muestran que la humedad relativa media mensual fue la variable que mejor explicó la dinámica de C. insignis en la zona de estudio. La transmisión de patógenos está probablemente influenciada por la abundancia del vector en el área. Los picos poblacionales observados indican los períodos donde debe haber mayor control para evitar la transmisión de la enfermedad. Este es el primer reporte sobre fluctuación poblacional de C. insignis en el noreste del país.Instituto de Limnología "Dr. Raúl A. Ringuelet

Fluctuación poblacional de Culicoides insignis (Diptera: Ceratopogonidae) en Posadas, Misiones, Argentina

The Bluetongue virus appears to be restricted in Argentina to the northeasternarea of the country. In the Neotropical region the main vector could be Culicoides insignis Lutz. This study was aimed to determine the population fluctuation of C. insignis in Posadas city and test the influence of climatic variables as determinants of the abundance of this species. The specimens were collected in Posadas city using CDC light traps from January to December 2013. The abundance of C. insignis in relation to environmental variables was analyzed using multivariate linear regression. A total of 2,952 specimens of C. insigniswere collected representing 93.4% of the total Culicoides captured. The multivariate linear regression analyses show that the monthly mean relative humidity was the variable that best explained the population dynamics of C. insignis in the work area. The pathogen transmission is probably influenced by the abundance of the vector in this area. The population peaks observed are indicative of periods when there should be more control to prevent transmissionof the disease. This is the first report of population fluctuation of C. insignis in northeastern Argentina.En Argentina, la distribución de la enfermedad del Virus de la Lengua Azul se encuentra restringida al noreste del país. En la región Neotropical el principal vector sería Culicoides insignis Lutz. El objetivo de este trabajo fue determinar la fluctuación poblacional de C. insignis en la ciudad de Posadas y también la influencia de las variables climáticas como determinantes en la abundancia de esta especie. Los ejemplares fueron capturados mediante trampas de luz en el período comprendido entre enero y diciembre de 2013. La relación entre el número de C. insignis capturados y las variables ambientales fue analizada por regresión lineal multivariada. Se recolectaron 2.952 ejemplares de C. insignis representando el 93,4% del total de Culicoides capturados. Los análisis de regresión lineal multivariada muestran que la humedad relativa media mensual fue la variable que mejor explicó la dinámica de C. insignis en la zona de estudio. La transmisión de patógenos está probablemente influenciada por la abundancia del vector en el área. Los picos poblacionales observados indican los períodos donde debe haber mayor control para evitar la transmisión de la enfermedad. Este es el primer reporte sobre fluctuación poblacional de C. insignis en el noreste del país.Instituto de Limnología "Dr. Raúl A. Ringuelet